Gleitlagerungen sind aufgrund ihres einfachen und robusten Aufbaus häufig verwendete Alternativen zu Wälzlagern. Flüssigkeitsgeschmierte Gleitlager lassen sich bzgl. ihrer Betriebsweise in hydrodynamische und hydrostatische Wirkprinzipien unterteilen. Aktuelle Entwicklungstrends, insbesondere bei Gleitlagerungen für Schiffswellen, fordern hohe Tragfähigkeiten bei reduziertem Platzbedarf. Gleichzeitig sollen Lagerungen eine hohe Robustheit bei minimalem Energieaufwand für die Schmierölversorgung aufweisen. Vorhandene technische Lösungen wie z.B. hydrodynamische Gleitlager werden diesen Anforderungen jedoch nur unzureichend gerecht. Beispielsweise weißen energetisch optimierte Systeme meißt eine unzureichende Robustheit oder einen sehr hohen Platzbedarf auf.

Im Rahmen des Forschungsprojektes HYDROS wurde ein Gleitlagerungssystem entwickelt, welches die Vorteile hydrodynamischer und hydrostatischer Wirkprinzipien kombiniert, um damit den aktuellen Forderungen gerecht zu werden. Ein daraus abgeleitetes Steuerungskonzept sieht eine bedarfsgerechte Schmierölversorgung der einzelnen Lagertaschen vor, welche durch ein vollkommen neu entwickeltes druckgesteuertes Schieberventil realisiert wird. Entsprechend des in der Lagertasche herrschenden Druckes erfolgt eine diskrete Steuerung des Zulaufwiderstandes und damit des Schmierölstromes. So wird der nicht benötigte Volumenstrom an den unbelasteten Lagertaschen abgeschaltet. Das in einem kompakten Patronendesign realisierte Ventil lässt sich seh einfach in die Lagerkonstruktion integrieren und übernimmt weitere Sicherheitsfunktionen wie z.B. die Gewährleistung des Notlaufbetriebes oder die Aufnahme von hohen Lastspitzen. Das bewusst einfach gehaltene Design garantiert eine hohe Robustheit und damit eine hohe Verfügbarkeit des gesamten Lagers.

Der Beitrag beschreibt zunächst die Funktionsweise sowie die spezifischen Eigenschaften des hydrostatisch-hydrodynamischen Kombilagers und geht im Weiteren auf die Funktion der Zulaufwiderstände ein. An den oben genannten Anforderungen werden mehrere Realisierungsmöglichkeiten der Zulaufwiderstände vergleichend bewertet. Aufgrund vielfältiger Vorteile wird auf die Variante mit druckgesteuertem Schieberventil (Druckwaage) tiefergehend eingegangen. Anhand ausgewählter konstruktiver Aspekte berichtet der Beitrag über die simulationsgestützte Auslegung und Dimensionierung des Ventils. Anhand von Messungen an den gefertigten Ventilprototypen wird die Funktionalität bewertet und mit den Ergebnissen der Simulation verglichen. Die vollständige Validierung der Steuerungsvariante mit den neu entwickelten Ventilen erfolgt an einem Lagerprüfstand im Maßstab 1:1. Anhand der Meßergebnisse wird die neu entwickelte Steuerungsvariante mit etablierten Lösungen verglichen und bewertet. Der Beitrag schließt mit einem Ausblick auf alternative Applikationsfelder ab.

Bei der Entwicklung von Regelungsansätzen zur hochgenauen Positionierung oder Trajektorienfolge mittels hydraulischer Zylinderantriebe spielt neben der geforderten Dynamik und Genauigkeit auch die Robustheit eine immer größere Rolle. Für sich wiederholende Positionieraufgaben oder Solltrajektorien sind iterativ–lernende Regelungen besonders gut geeignet, verbleibende Modellfehler oder unbekannte konstante Störeinflüsse zu kompensieren und liefern bereits nach wenigen Iterationen sehr geringe Positionier- bzw. Trajektorienfolgefehler. Hierzu werden insbesondere Informationen zu den Regelfehlern aus vorherigen Durchläufen genutzt und im aktuellen Zyklus zu einer Korrektur des Stellgrößenverlaufs verwendet. Ein allgemeiner Überblick über iterativ lernende Algorithmen wird in [1] und [2] gegeben.

Im vorliegenden Beitrag wird eine normoptimale iterativ-lernende Trajektorienfolgeregelung [3] auf Basis eines nichtlinearen regelungsorientierten Modells für einen servo–hydraulischen Zylinder – nachfolgend als Positionierzylinder bezeichnet – entworfen und an einem Prüfstandsaufbau experimentell validiert. Der zur Validierung des Regelungskonzepts verwendete Prüfstandsaufbau besteht aus zwei gekoppelten hydraulischen Zylindern: Auf der linken Seite ist der positionsgeregelte Positionierzylinder dargestellt, welcher durch ein Proportionalventil angesteuert wird. Zur reproduzierbaren Einprägung nachgebildeter Störkraftverläufe auf den positionsgeregelten Zylinder dient ein hochdynamischer, kraftgeregelter Servozylinder. Die Kraftregelung wird in diesem Beitrag durch einen modellbasierten nichtlinearen Ansatz realisiert, der Rückwirkungen infolge der Verschiebung durch den Positionierzylinder berücksichtigt.

Der Beitrag gliedert sich in die folgenden Abschnitte: Nach einer kurzen Einleitung, in der die Problemstellung erläutert wird, wird die regelungsorientierte Modellbildung des Prüfstands beschrieben, wobei vorteilhaft eine Aufteilung in ein hydraulisches und ein mechanisches Teilsystem vorgenommen wird. Die Modellbildung führt auf ein System von nichtlinearen gewöhnlichen Differentialgleichungen. Aufbauend auf dem Entwurfsmodell werden für den Positionierzylinder eine Positionsregelung auf Basis einer normoptimalen iterativ–lernenden Regelung und für den Servozylinder eine modellbasierte Kraftregelung entworfen. Die Implementierung der Prüfstands–Regelungsstruktur zeigt einen schnellen Abfall des Trajektorienfolgefehlers bei mehrfachem Durchlaufen einer vorgegebenen Solltrajektorie. Bei unbekannten, aber sich wiederholenden Störkraftverläufen verschlechtert sich zunächst das Folgeverhalten; bereits nach wenigen Iterationen kann aber mit dem vorgeschlagenen Regelungskonzept wieder ein präzises Folgeverhalten auf dem Niveau vor Aufschaltung der Störkraft erreicht werden. Es zeigt sich weiterhin, dass die erzielten maximalen Trajektorienfolgefehler deutlich unter denen einer Kompensationsstrategie mittels Störbeobachtern liegen.

Literatur:
[1] D.A. Bristow, M. Tharayil, and A.G. Alleyne: A survey of iterative learning control. IEEE Control Systems Magazine, 26(3):96-114, 2006.
[2] K.L. Moore: Iterative learning control: An expository overview. Applied and Computational Control, Signals and Circuits, 1:151-214, 1999.
[3] N. Amann, D.H. Owens, and E. Rogers: Iterative learning control for discrete-time systems with exponential rate of convergence. IEEE Proceedings: Control Theory and Applications, 143(2):217-224, 1996.

The metal powder compaction (MPC) presses driven by electro-hydraulic servo system (EHSS) without mechanical limit of the die offer several advantages over the ones driven by on-off hydraulic system with die limit in manufacturing many classes of powder forming products. The former ones make the process of production more flexible, as a result, it is more feasible and more efficient to produce various shapes of parts. The quality of green compacts is also higher. To improve the quality of green compacts produced further, bidirectional pressing and floating pressing are required in manufacturing process, thus the proposed MPC press is configured with two punches (named upper punch and lower punch) driven by two EHSSs respectively. To guarantee these advantages, precise force/motion control of the two punches is crucial. It is a challenging work to design a well performed controller for the proposed press due to multivariable regulation and coordinate of multi-actuator in the sophisticated forming process as well as high nonlinearity and parameter uncertainty of the hydraulic system etc. To address all these issues, a systematic MIMO adaptive robust control (ARC) method is employed in this paper. First, a control oriented model is constructed to describe the system dynamics concerning the nonlinearity and parameter uncertainty. Then the model is divided into two subsystems corresponding to EHSSs respectively. Force regulation and motion control are assigned to the two subsystems separately. It is obviously that the whole system is a typical MIMO nonlinear system with semi-strict feedback form. At last, ARC control law, which achieves disturbance rejection by robust term and estimates uncertain parameter on-line by adaptive law, is derived by backstepping design based on Lyapunov function. With the resulting ARC control law plus trajectory initialization applied, the stability, tracking transient and final tracking accuracy are guaranteed. Examples are performed on a 1000kN MPC press prototype, and the results validate the effectiveness of the proposed ARC controller in practical application.

This study aims to develop a leveling position control and anti-vibration control of the four-axial pneumatic isolation table system with novel PWM-driving parallel dual-on/off Valves. A novel concept using parallel dual-on/off valves with PWM control signals is implemented to realize active control and to improve the conventional pneumatic isolation table that supported by four pneumatic cushion isolators. In this study, the cushion isolators are not only passive vibration isolation devices, but also pneumatic actuators in active leveling position control and anti-vibration control. Four independent closed-loop position and velocity feedback control system are designed and implemented for the four axial isolators. In the controller design, the adaptive sliding-mode controller is used to deal with the uncertainty and time-varying problems of pneumatic system.
Finally, the experiments on the four-axial pneumatic isolation system for the synchronous position and trajectory tracking control as well as the anti-vibration control, including no-load and loading conditions. The synchronous position control with master-slave method is also implemented in order to verify that the controller for each cushion isolator can realize good performance of the leveling position control and the anti-vibration control.

Vakuumhandhabungstechnik nimmt in vielen Bereichen des industriellen Materialflusses eine unersetzbare Rolle ein. Aufgrund der Unzugänglichkeit für andere Greifprinzipien und/oder der schonenden Handhabungsform ist die Vakuumhandhabungstechnik in Anwendungsfeldern wie Logistik, Blechhandhabung oder dem Verpackungsbereich nicht wegzudenken. Die Vakuumerzeugung kann dabei auf zwei grundsätzlich unterschiedliche Arten erfolgend. Zum einen können je nach Anforderung an Volumenstrom oder Unterdruck Pumpen oder Gebläse eingesetzt werden, zum anderen ist die Vakuumerzeugung mittels druckluftbetriebener Ejektoren möglich. Hierbei werden Venturi-/Laval-Düsen verwendet um ein für die Handhabung ausreichenden negativen Überdruck zu erzeugen.
Da es sich bei Handhabungsaufgaben meist um nicht wertschöpfende Prozesse handelt, wird von Seiten der Anwender versucht den Energieverbrauch auf das Nötigste zu minimieren. Hierbei spielt die Auswahl der Vakuumerzeugung eine entscheidende Rolle, da diese den energieintensiven Teil des Vakuumhandhabungssystems darstellt. Aufgrund der Unsicherheit des Vergleichs der verschiedenen Erzeugungsarten soll in dieser Arbeit eine Methodik vorgestellt werden, mit deren Hilfe sich beide Arten der Erzeugung – elektrisch und pneumatisch – energetisch Vergleichen lassen. Wichtig ist dabei die ganzheitliche Sicht der Betrachtung, sodass beide Gesamtprozesse vergleichbar werden. Besondere Beachtung wird dabei der pneumatischen Vakuumerzeugung geschenkt, da diese u.a. durch den vorgelagerten Kompressor ein komplexeres System als die rein elektrische Erzeugungsart darstellt.
Auf Basis des Energievergleichs der beiden Systemalternativen können in weiteren Schritten auf einfache Art eine Gesamtkostenrechnung (LCC) oder Ökobilanz (LCA) erstellt werden, welche somit neben den rein technischen Anforderungen an das Handhabungssystem ebenfalls in die Systemauswahl einfließen können.

In der industriellen Automatisierung kommen elektromechanische und pneumatische Antriebe zur Realisierung von verschiedenen Bewegungsaufgaben zum Einsatz. Pneum. Antriebe zeichnen sich, im Vergleich zu elektromechanischen Antriebslösungen, durch einen geringen Anschaffungspreis und niedrige Wartungskosten aus. Hinsichtlich des Energieaufwands gibt es eine Vielzahl von Maßnahmen um effizient zu arbeiten, aber die Frage nach der Bewertung des Energieverbrauchs ist nach wie vor Gegenstand der Forschung.

In mehreren Forschungsprojekten wurde bereits gezeigt, dass Druckluftanlagen und pneum. Verbrauchersysteme oft große Einsparpotenziale aufweisen. Diese Einsparpotenziale können durch den Einsatz von Energiesparmaßnahmen genutzt werden, welche beispielsweise auf eine Reduzierung des Betriebsdrucks abzielen. Für eine effiziente Umsetzung dieser Maßnahmen muss das Einsparpotenzial eines jeden Antriebssystems bekannt sein. Dazu muss eine Analyse des energetischen Systemverhaltens durchgeführt werden.

Für die energetische Analyse eines pneumatischen Antriebsystems bieten sich drei verschiedene Methoden an. Diese drei Methoden sind die Druckluftverbrauchsrechnung, die energetische Bilanzierung mithilfe der Kenngröße „Air Power“ und die Exergie-Analyse. Diese Methoden basieren auf den thermodynamischen Grundlagen pneumatischer Systeme. Die Berechnungsgleichungen der einzelnen Methoden unterscheiden sich hinsichtlich ihrer Komplexität und gelten unter unterschiedlichen Randbedingungen.

Die Methoden wurden bereits einzeln in Veröffentlichungen vorgestellt.
Im Gegensatz dazu zielt dieser Beitrag auf die Gegenüberstellung dieser Methoden ab. Im geplanten Beitrag erfolgt zunächst eine Beschreibung der verwendeten Berechnungsgleichungen und getroffenen Annahmen. Danach wird die Eignung der jeweiligen Methodik zur Detektion von Einsparpotenzialen und zur Ableitung von Energiesparmaßnahmen aufgezeigt.
Dabei wird untersucht, ob durch die Verwendung einer komplexen Exergie-Analyse zusätzliche Potenziale gefunden werden können. Schließlich wird die Anwendbarkeit der Methoden in einem industriellen Umfeld untersucht. Hierbei wird beispielsweise der benötigte Aufwand zur messtechnischen Erfassung der Bilanzgrößen der jeweiligen Methode verglichen.

Bei der Druckluftverbrauchsrechnung wird die Befüllung der vorhandenen Zylinder-, Schlauch- und Totvolumen auf einen gewissen Betriebsdruck innerhalb eines Arbeitszyklus betrachtet und das benötigte Druckluftvolumen bestimmt. Bei den Befüllungsvorgängen wird ein isothermes Zustandsverhalten (T = konstant) angenommen. Diese Methode ist für die Bestimmung der Energieaufnahme pneumatischer Antriebe mit einfachen Schaltungsstrukturen (z.B. abluftgedrosselter Zylinderantrieb) geeignet, jedoch nicht für die Beschreibung von Verlusten.

Sowohl bei der Analyse mittels Air Power als auch Exergie wird die pneum. Energie quantitativ auf der Basis des 1. Hauptsatzes der Thermodynamik und qualitativ auf der Grundlage des 2. Hauptsatzes der Thermodynamik bilanziert.

Die Air Power beschreibt den maximalen Anteil an technischer Arbeit, welcher aus einem Druckluftstrom gewonnen werden kann. Die Herleitung der Kenngröße erfolgt aus der Bestimmung der maximal umsetzbaren Arbeit unter isothermen Randbedindungen an einem Kolbenzylinder. Die Kenngröße Air Power setzt sich aus einem Expansionsanteil und einem Verschiebeanteil der pneum. Leistung zusammen. Weiterhin berücksichtigt diese Beschreibung Verluste durch Entropieproduktion.

Der dritte Ansatz zur Energiebilanzierung ist eine Exergie-Analyse, welche auf die Bilanzierung der Exergie innerhalb des Systems abzielt. Die Exergie ist der Anteil der pneum. Energie, welcher für die Umwandlung in technische Arbeit genutzt werden kann. Die benötigten Berechnungsgleichungen bei einer Exergie-Analyse sind aufwendiger als bei den ersten beiden Methoden, berücksichtigen jedoch das Temperatur¬verhalten des Antriebs und erlauben die Quantifizierung aller thermo¬dynamischen Verlustanteile.

During the last years, lightweight construction using sheet metals manufactured by hot stamping increased permanently. Especially the automobile industries applies hot stamping as forming method to save weight in the car structure. Hot stamping is a forming process with hot metal sheets in the temperature range of 600-950°C. The thermal shock in the forming die causes the microstructure of the metal sheet to transform from austenitic to martensitic crystal structure, resulting in high strength.

Bulge tests are used to examine material properties as flow curve and FLC of sheet metals. In contrast to common tensile tests, higher strains can be achieved using the bulge test because of its biaxial stress characteristics. The exact knowing of the material behavior is a fundamental factor for improving finite element simulation. More accurate simulations for the forming processes can reduce material and development costs at the same time.
In this paper a new approach of the hot gas bulge test is presented to match the conditions for hot stamping.

In cold bulge tests the metal sheet is formed using hydraulic oil under high pressure at cold temperatures. However, the mechanical properties of most metals exhibit an increasing dependence on the strain rate at higher temperatures. The application of hydraulic oil at temperatures in the range of 600°C to 950°C is not possible, so the need of another pressure medium is necessary. Since the forming should be frictionless to avoid an impact of the contact material, inert gas is chosen as pressure medium.

The required temperatures of the metal sheet between 600°C-950°C, different forming speeds with controlled strain rates, high pressure and physical properties of gases as well as safety and noise aspects create a challenging task for the design of the test chamber and pressure control. Existing gas based bulge tests at high temperatures are not able to control strain rates, nor to form the test samples at high strain rates.

The dimensioning is based on the process sequence in correlation with the volume change of the bulge. The bulge volume influences directly the amount of energy stored within the test chamber. Due to the compression capability of gases, the gas volume can cause an overcritical bulge, if the metal strength decreases more rapidly by strain than the gas pressure by volume expansion. An exact design of the chamber is necessary to avoid an uncontrolled failure of the samples.

Different concepts of design and control are reviewed to find the best fitting solution for the new hot gas bulge test. A simulation analysis of the flow curve with extrapolated parameters reveals required conditions on a pressure control valve to provide the needed mass flow rates. The realization of the test chamber and the layout of the control circuit are presented. The pressure control must handle high mass flow rates for high strain rates as well as exact amounts of very small mass flow rates for slow forming cycles.

Screw pumps are low-noise and theoretical pulsation-free positive displacement pumps. They are used in oil and chemical industry, as fuel supply and injection pumps in marine and gas turbine applications, as lubrication pumps and as well as hydrostatic drive for presses and elevators.

Screw pumps show a pressure operation limit resulting from lateral hydrostatic loads on the sidewise idle screws. The hydrostatic forces are balanced by hydrodynamic journal bearing forces in the chamber sealing gaps between spindles and casing.

At the chair of Fluid Systems Technologies at Technische Universität Darmstadt a hydrostatic load balance of the idle screws inside the delivering area of the screws has been developed and two prototypes have been build and tested. The system uses the potential of suction and discharge pressure of the pump, and sets compensation pressure on the exterior diameter of the idle screws. Due to the fact that the chamber sealing changes position in axial direction the compensation pressures are switched by the turn angle of the screw itself. Hence the compensation system is passive. Measurements showed a very small additional inner leakage.

The system vanishes hydrostatic loads and enables to drive screw pumps within higher differential pressures.

In hydraulic pumps and motors, the tribological contacts are responsible for the greatest share of hydromechanic and volumetric losses. The most important tribological interfaces in an axial piston machine are the contacts piston / cylinder, cylinder block / valve plate and slipper / swash plate. Other tribological interfaces have minor importance in ordinary operating points.

In the past, a couple of simulation approaches have been presented for simulating the tribological contacts of axial piston machines. These approaches have different conditions and goals considering different physical effects. In all simulation approaches, the Reynolds equation which describes the characteristics of the fluid film is taken into account. Moreover deformations as well as the micro-movement of the involved parts, thermic effects, cavitation, solid contact and mixed friction can be considered. The friction torque between cylinder block and valve plate consists of viscous and solid friction. For high operating speed viscous friction is dominant, while for lower speed mixed friction becomes more relevant.

In this paper, a simulation model for the tribological contact cylinder block / valve plate is presented. Micro movement of the cylinder block and models for solid contact and mixed friction are implemented, so that it is possible to run realistic simulations for high and low speeds. Moreover, geometric variations of parts in an axial piston machine are simulated. The simulative results are compared and discussed with regard to friction and leakage losses.

Noise emission of hydraulic drives represents a major subject in many applications. As hydraulic pumps are the primary source of oscillations leading to noise, present major issues in pump development are minimizing the flow ripple and the resulting pressure pulsation as well as reducing direct oscillations of the mechanical structure. For this reason, pump simulations have become more and more important. The variety of model types ranges from simple and universal approaches concentrating mostly on the flow ripple up to construction specific models with respect to both, structure and fluid mechanical effects.
Whereas complex, construction specific simulation models work with tree-dimensional design aspects of the pump, more simple and universal models try to describe certain functional characteristics by defining less complex, two-dimensional parameters, such as the volume of one displacement chamber relative to the driveshaft angle or the variations of areas for flow transfer between chamber and ports. This type of model is rather common in today’s industrial development.
Insofar as the shapes of displacement chamber and corresponding elements can be described by simple mathematical functions, simulation parameters can be derived easily from the dimensions of the related design elements. A good example of such pump geometry is an axial piston machine with circle-shaped endings of ports and chamber opening as well as symmetric pre- and decompression grooves. If the shapes of displacement chamber and ports are more complex and difficult to describe by means of mathematical functions, the simulation parameters cannot be linked directly with dimensions of design elements. Typical examples of these geometries are gear pumps. In this case, parameters have to be calculated by approximation. Finding an appropriate software solution for this is important, because with every change in the functional design of the pump one or more simulation parameters have to be recalculated.

In this paper, a fast and universal method for deriving two-dimensional simulation parameters from complex pump geometries will be presented. The method provides two types of information. First, a modular structure that allows to easily build up a parameterization tool for any pump geometry. This can be seen already on a very high level, where every single parameterization procedure consists of modules for assembly, motion and calculation of the demanded output. Secondly, the method offers a set of algorithms for the calculation of closed and partial functional areas, as well as algorithms for position calculation of pump elements that have to be positioned in an iterative way on the basis of certain conditions of contact. A typical example for this need is the relative angular positioning of gears or vanes. By defining the cutting points between the calculation modules just on the basic principle of hydrostatic pumps, the method is applicable to different types of pumps, taking gear and vane machines as examples. Even combined functional principals are covered.
The presentation will start with a short introduction to the general approach of modeling pumps by defining two-dimensional parameters. After that, the overall concept of the method will be explained by showing, how the modular structure of parameterization can be adapted to different types of pumps. This will be followed by a closer look at some of the algorithms used in this method. By taking one complex pump geometry as an example, specific calculation results for common parameters will be discussed, such as the variations of displacement chamber volume and flow transfer areas. At this point, the main focus will be laid on accuracy and calculation which usually represent the most interesting aspects within the industrial development process. At the end of the presentation, the potential of the method for deriving additional, new parameters will be estimated.

Oil pumps, including vane, gerotor, crescent and external gear pumps, are a critical component in many industrial applications. Generated rotor (gerotor) pumps are internal rotary positive-displacement pumps in which the outer rotor has one tooth more than the inner rotor. The inner and outer gear tooth profiles are described by epitrochoidal equidistance and circular arcs respectively.
Due to their compact design, low cost, and robustness gerotor pumps are commonly used for cooling, lubrication, and filtration systems, for pumping liquids such as oil, transmission fluid, and fuel. They provide high volumetric efficiency and smooth pumping action and they work well with a wide range of fluid viscosities.
In this paper a new gerotor pump with innovative gerotor design is presented and fundamentally investigated by means of full three dimensional transient Computational Fluid Dynamics (CFD) analysis. Five gerotor pump CAD models (having from 8 to 12 teeth of the internal gear and from 9 to 13 teeth of the external gear) were designed and compared to a standard gerotor pump (having 8 inner rotor and 9 outer rotor teeth). The results from the simulation showed a substantial reduction of the flow and pressure ripple of all five models. Furthermore the flow rate and the volumetric efficiency of all gerotor pump models were predicted. Finally a prototype of the first CAD model was built and its simulation results were compared to the experimental data with excellent agreement.

Mobile hydraulic applications distinguish themselves from other hydraulic applications, such as industrial hydraulics, because the pressure and flow demand varies greatly over time and between different functions. Unlike other hydraulic applications, several functions are often supplied by one single pump. This means that the total installed power on the actuator side is generally considerably higher than the installed pump power. This is possible because the actuators almost never require their maximum power at the same time.

Given these conditions, the development of working hydraulic systems has moved towards load sensing systems. These systems have high energy efficiency since the pump pressure continuously adapts to the highest load. However, load sensing systems suffer from poor dynamic characteristics due to their closed loop pressure control. In specific points of operation, load sensing systems can thereby display oscillatory behaviour.

Another pump control strategy is to remove the load sensing hose and control the pump according to the operator’s command signals. The pump displacement setting is then controlled according to the sum of all requested load flows. This is a change from a closed loop control mode to an open control mode with no feedbacks present. It makes the system design process simpler since the pump can be designed to meet the response requirements without considering system stability.

There are several challenges with an open pump control strategy. One of them is to match the pump flow and the expected load flows, often referred to as flow matching. This problem occurs if the valves are equipped with traditional pressure compensators, controlling the absolute flow through the directional valve. If the flow sent by the pump is higher than the sum of all load flows, the pump pressure will increase until the system relief valve opens and the system will emerge as a constant pressure system. There exist several workarounds to this problem. Feedback signals could be introduced by using sensors or the system could be complemented with a bleed-off valve. Another solution is to use flow-sharing pressure compensators, distributing the entire pump flow relative to the individual valve openings. A drawback with flow sharing compensators is that the highest load dynamically will disturb all lighter loads.

This paper presents another solution to the flow matching problem. Instead of being flow or pressure controlled, the pump could be controlled partly by pressure and partly by flow. Load sensing systems and flow on demand systems are extreme points on this continuous scale. From a control theory point of view, pressure control would be the feedback gain and flow control would be the feed forward gain. By using this hybrid pump control approach, it is possible to take advantage of the benefits with load sensing and flow on demand and at the same time avoid their drawbacks.

The benefits and drawbacks with the respective system design are shown and demonstrated in this paper. One way of finding the optimal control parameters for pressure and flow control are proposed. A higher feed forward gain will increase the system response but exacerbate the problem of flow matching. A higher feedback gain will solve the flow matching problem but the system will get more oscillative. The user benefits of optimal control parameters are fast response, high stability and high robustness.

In this paper, both theoretical studies and practical implementations demonstrate the capability of a hybrid pump control approach. Experiments show that it is possible to improve the system characteristics by finding the optimal compromise between pressure and flow control.

Hydraulic control system is the most important transmission of construction machinery due to its high power density. Many hydraulic circuits, such as open center systems, load sensing systems, flow sharing systems, have been developed in the past few decades. However, these mobile hydraulics should be more efficiency to reduce combustion emission imposed by government legislations. The electronic flow matching control (EFMC after)system, which works in a synchronous mode of electrohyraulic valves and electrohyraulic pumps, has been a research focus in recent years because of its potential to improve the control performance and energy efficiency in comparison of the current mobile hydraulics.
In this paper, to improve the energy efficiency of mobile hydraulics, a flow sharing control system with electronic flow matching is developed, also a novel flow dividing algorithm is proposed to reduce the pressure loss of the control valve. The flow sharing system with electronic flow matching consists of an electrically controlled pump, a relief valve, proportional directional valves, post compensated valves and actuators. The working conditions of flow saturation and typical digging cycles were experimentally investigated on a mini excavator test bench. The results indicated that compared with the conventional flow sharing system in typical digging tests, the energy consumption of the proposed system was reduced by 10%.
In the traditional way, the control signals from the input devices, like joysticks, are directly delivered to the valves or pumps. In this study, a new flow dividing algorithm is proposed for efficiency improvement. Firstly, the controller selects the actuator with highest flow demand, and then the maximum signal is given to the corresponding control valve to fully open it. The control signals of the other valves are modified proportionally according to the control inputs. Based on the anti-saturation ability of flow sharing valves, the operation performance by the proposed method is in accordance with that by the traditional method. Meanwhile, the pressure loss of the directional valve by the proposed method is reduced due to the larger cross-sectional area, therefore the energy efficiency is improved. The experimental results indicated that the energy efficiency was improved by 13% with the proposed method.
The rest of the paper is structured as follows: Firstly the system configuration of the flow sharing system with electronic flow matching is introduced , and then the simulation model is built up in section 2. Section 3 describes the simulation and experimental results to compare the conventional flow sharing system with the proposed system. Section 4 gives the introduction of the proposed flow dividing algorithm and the experimental tests in comparison of the traditional control method. Section 5 describes the conclusions and future works.

This paper presents an innovative experimental auto-tuning method of a controller used to operate an electro-hydraulic crane with the aim of reducing system oscillations. Commonly, the control tuning is conducted using two different strategies: analytical derivation from system model, or trial-and-error based methodologies, in many cases applied directly on an experimental set up. Both mentioned approaches are in most of the cases time consuming and sometimes inaccurate. For the first approach, the analytical derivation may lead to poor control performance in case of inaccurate model parameters estimate, while, for the second case, there is often not guarantee the controller parameters are optimal.
The proposed auto-tuning method is applied to a particular control strategy developed by the authors to reduce oscillations in mobile hydraulic machines. The pressure feedback control method, presented in [1] solely requires pressure sensors mounted on the workports of the flow control valves of the hydraulic system. Despite the generality of the proposed technique, this paper presents the application of the controller, and of the novel auto-tuning method, on the particular case of the mechanical arms of an hydraulic crane installed at Maha Fluid Power Research Center of Purdue University.
The experimental-auto-tuning method proposed in this research in based on an iterative loop in which the optimal control parameters are found through an optimization process. The process iterations are represented by real experiments. At each iteration, the effectiveness of the controller is evaluated through a proper objective function used to quantify the system oscillations. The control performance is measured as deviation of the actual dynamics from the ideal one, in terms of system acceleration. Also, the procedure always verifies that the considered control parameters always meet the requirements in terms of machine productivity. Particular effort is dedicated to the optimization procedure used to minimize the total number of experiments to be performed in a fully automated tuning procedure.
The paper describes the control performances in terms of measured acceleration of the mechanical arms for different drive cycles of the machine taken as reference. The results show also the capability of the presented tuning method to produce better control performance with respect to a traditional tuning method previously utilized to control the reference machine.
The proposed experimental-auto-tuning method has potential to become an industry practice since it offers an automatic and time-effective way to tune the control parameters of any electro-hydraulic machine, without requiring significant expertise in the controller design.


References:
[1] Cristofori D., Vacca A., 2012, A Novel Pressure-Feedback Based Adaptive Control Method to Damp Instabilities in Hydraulic Machines, SAE Int. J. Commer. Veh. 5(2):2012.

Steering systems of mobile machinery have not seen adequate innovation and breakthroughs in the past few decades, except for a few incremental developments. Hydrostatic steering dominates the state-of-the-art, and is ubiquitous on most agricultural and construction machinery. This paper introduces an innovative steering concept for articulated frame machines, namely wheel loaders. The new system is based on pump displacement control (DC), a well-established energy efficient alternative to valve control. DC technology has been successfully researched and applied to the implement functions (working hydraulics) of mobile machinery resulting in significant fuel savings. However, DC has never been investigated for the steering function of such machines, which is the focus of the research conveyed in this paper.
In addition to its potential fuel savings, a DC steering system also promises multiple other advantages in regards to machine safety, productivity, packaging, and comfort. DC steering can be classified as an electrohydraulic steer-by-wire system, which offers the numerous benefits, and challenges, typically associated with by-wire systems. On top of improved fuel economy, a DC steered machine can be made safer via active steering intervention to stabilize lateral instabilities and reject external disturbances. Also, DC steering increases the productivity and safety of the machine by employing variable-rate / variable-effort steering algorithms, which adjust the sensitivity and gain levels based on the machine’s operating conditions. At low vehicle speeds the number of steering wheel turns and the amount of torque feedback are reduced, resulting in reduced operating time per unit work as well as reduced operator fatigue. On the other hand, the number of steering wheel turns and the amount of torque feedback are increased to prevent sudden steering perturbations from destabilizing the machine while traveling at high speeds.
To permit for generating appropriate control algorithms that offer suitable performance, a high fidelity dynamic model of the ‘plant’ had to be developed. The plant model constitutes of two main subsystems: an electrohydraulic component and a mechanics one. The electrohydraulic module includes models of the variable axial piston pump, pump adjustment system, low pressure system, steering actuator, and others; whereas the mechanics module includes an advanced multi-DOF vehicle dynamics model based on the Lagrangian principle. Complex nonlinear models were first generated, after which linearized models were developed and validated, paving the way in front of controller synthesis and design.
Modern control theory techniques were utilized for controlling the linear time invariant (LTI) system. State space formulation was facilitated by the system of linear first order differential equations derived for the two subsystems. Controller design focused on the following approaches: full state feedback, reference tracking, output feedback, and state observer/estimator design to reduce the number of required sensors by employing virtual sensing instead. Attention was then turned to the controllable part of the system where the input (pump displacement) results in a direct adjustment of the desired output (articulation angle).
A designated test vehicle, a wheel loader, has been baseline tested with its stock hydrostatic steering system and is currently undergoing the necessary hardware and software modifications for implementing the new DC steer-by-wire system. Upon completion, the machine will be retested at which point the generated models and the designed controller will be validated and fine-tuned. The measurement and simulation results will be included in this paper.

This paper investigates the effect of hydraulic oil on the efficiency of an electro-hydraulic forklift with lithium-titanate battery. The control of the system is implemented directly with a motor drive without conventional control valves. The measurements with two oils, a conventional multigrade hydraulic oil and a high performance hydraulic oil were carried out using the two lifting zones of the forklift. The paper provides accurate evaluation of the hydraulic system and a detailed analysis of the properties of the hydraulic oils before and after use in the mobile working machine. Finally, efficiency improvements in the suggested system are observed.

Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. To ensure safe and reliable functioning of the new fuels in combination with state of the art fuel injection equipment, every fuel has to fulfill minimum requirements regarding lubricity. Hence, one focus of the cluster lies on the tribology of the fuel candidates.
Compared to diesel fuel the so far investigated biofuels differ strongly in their rheological characteristics. To investigate the impact of the fuel candidates on the tribological contact in standard common rail pumps a single-piston-test-rig was set up. The rig allows the measurement of friction forces in a piston/bushing-contact under realistic operating conditions. In the test rig all components of the relevant fuel lubricated contacts are original parts from the common injection pumps. In this paper results of measurements for different fuel candidates and pump operating points are presented and compared to the result of laboratory scale lubricity test methods like the well established HFRR-test.
In parallel to the experiment an elastohydrodynamic simulation model for the single-piston-test-rig is presented. The simulative outcome is compared to measurement results from the test rig.
The paper ends with a critical discussion based on experimental and simulative results regarding the validity of the simple pass/fail criterion defined in several norms for evaluating diesel fuel lubricity for the investigated low viscosity fuel candidates.

Environmental protection regulations are becoming increasingly strict. However, by using water instead of a hydraulic mineral oil in power-control hydraulic systems we can make a very positive step towards complying with these regulations. Nevertheless, using water instead of oil in power-control hydraulics is a novel and difficult task. Moreover, due to some specific characteristics of water, several requirements need to be fulfilled in every test rig and test specimen. On the other hand, the storage and regeneration of energy is also very important.

In this paper we present a newly developed water hydraulic accumulator. This piston-type of water hydraulic accumulator was designed to match the requirements mentioned above using water as the hydraulic liquid. The new water hydraulic accumulator has a volume of 4 litres and an allowed maximum pressure of 390 bar. A prototype was manufactured and a certificate was acquired from the European pressure directive PED 97/23/EC.

The new water hydraulic accumulator was designed, manufactured and tested by the Laboratory for Power-Control Hydraulics. This water accumulator was constructed so that we could simply exchange its sealings and/or guiding to investigate the tribological and hydraulic behaviour of the sliding contacts.

The results based on the hydraulic dynamics and thermodynamic changes of the gas in the hydraulic accumulator using two different hydraulic liquids (distilled water and mineral hydraulic oil) are presented and compared for three different pressures of nitrogen (30, 60 and 90 bar) and four different thermodynamic processes. The results show significant differences in the tested hydraulic accumulator efficiency between the slow thermodynamic transformation (isothermal process) and the fast adiabatic process.

The results indicate we should be optimistic about the use of the new water hydraulic accumulator in the field of water hydraulics in general.

Under low-speed high-torque conditions, hydraulic motors operate in the boundary lubrication regime. As a result, lubricating oil additives can affect friction and efficiency. This paper presents an investigation of boundary additive film formation, friction, and surface topography in benchtop tribometers and hydraulic motors. The mechanical efficiencies of geroler, axial piston, bent axis, and radial piston motors were measured under low-speed, high-torque conditions. The addition of a friction modifier to an ashless hydraulic fluid increased the efficiency of the motors at low speed. EDX analysis of motor surfaces after testing revealed the presence of tribochemical films from the hydraulic fluid additives. The ratio of additive elements to base metal was higher for the ZDDP fluid than the fluid formulated with ashless additives. AFM and 3-D surface mapping of tribometer surfaces revealed that the friction modifier reduced the surface roughness variation of the wear scar. The friction modifier also increased wear and reduced the concentration of phosphorus on the surface. These findings are significant because they provide insights to the development of fluids that can enhance motor efficiency.

Growing awareness of climate change, and an increase in fuel prices, has sparked a renewed interest in hybrid vehicle technologies. While electric hybrids have thus far received most of the attention, hydraulic hybrids have shown significant benefits especially for larger vehicles. Currently a number of architectures exist for hydraulic hybrid transmissions, each with their own benefits and deficiencies. One of the most popular architectures known as a series hybrid suffers from periods of low efficiency due to continual operation at high minimum system pressures, poor torque response when the required pressure is higher than the current system pressure, and the requirement for more expensive over-center units.

The authors have previously presented a novel blended hybrid system architecture which addresses the aforementioned deficiencies. This novel architecture blends components of a hydrostatic transmission and a parallel hybrid thereby increasing system efficiency and response to levels greater than either transmission could provide individually. The hydrostatic path improves efficiency over series hybrids by permitting the system to operate at the lowest required pressure for a given load. Additionally the hydrostatic path improves response and user feel to that of a mechanical transmission. Further a series of check valves removes the need for over-center units while braking. Finally a second set of check valves allow engine and accumulator power to be combined together while still maintaining a stiff and responsive system.

Power split transmissions (PST) represent the next generation of hydraulic hybrid architectures. They combine the flexibility and energy recovering potential of series hybrids with the efficiency of a pure mechanical transmission. In this paper the authors will incorporate the previously introduced blended hybrid into the hydraulic path of a power split transmission. A baseline automatic transmission, a traditional hydraulic hybrid PST, and the novel blended hybrid PST will be modeled and simulated in a class II truck.

Previous research has demonstrated the major influence controller design has on fuel economy. In fact a poor system architecture with good control can outperform a superior system architecture utilizing a substandard controller. To ensure a fair system comparison dynamic programming will be used to optimally control all three transmissions, thereby removing the effect of controller design on fuel consumption. The authors will conclude the paper with a detailed analysis and comparison of the three system architectures

Aktuelle Herausforderungen für ventilgesteuerte hydrostatische Verbraucher ist die Minimierung der energetischen Verluste entlang des Steuerstrangs, die Erhöhung der Positioniergenauigkeit und der Stellzeiten im Kontrast zum Streben nach kostengünstigen und robusten Systemen. Die Freiheitsgrade dieses Optimierungsproblems sind sowohl komponenten- als auch regelungstechnischer Art. Ventile mit aufgelösten Steuerkanten zur getrennten Regelung von Vor- und Rücklauf und die daraus hervorgehende Einführung digitaler Ventiltechnik sind die technischen Träger des Fortschritts. Neue regelungstechnische Methoden, wie beispielhaft die Nutzung der Eigendynamik eines Ventils durch die Ansteuerung mit einem Signalimpuls, werden dem großen Komponentenspielfeld überlagert. Für den Planer hydraulischer Anlagen ergeben sich so unüberschaubare Arbeitsfelder, eine objektive Systemauslegung unter Berücksichtigung aller Möglichkeiten ist nicht realisierbar. Dem Ingenieur kann hier kein Vorwurf gemacht werden, da kein geeignetes Werkzeug zur Verfügung steht, um die Topologie eines Systems in Frage zu stellen, sondern lediglich Parameteroptimierungen automatisiert durchgeführt werden können.

Am Institut für Fluidsystemtechnik wird eine innovative Methodik zur Systemauslegung entwickelt: Technical Operational Research (TOR) sieht im Kern folgendes Vorgehen zur Auflösung der nicht-trivialen Problematik vor: Der erste Schritt der Systemauslegung ist immer die Klärung der grundlegenden Funktion des Systems. Anschließend folgt die Frage nach dem Ziel der Planung. Dieses Ziel ist immer subjektiv und erfordert vom Planer eine Positionierung des Projekts im Zwiespalt von Energieeffizienz, Robustheit, Genauigkeit und Kosten. Der zur Erfüllung von Ziel und Funktion vorhandene Komponentenbaukasten wird im nächsten Schritt beschrieben. Dazu werden die Gleichungen zur Beschreibung einer Komponente formuliert. An dieser Stelle sind alle Entscheidungen zur Auslegung des Systems getroffen, aber dessen Struktur noch unbekannt. In einem weiteren Abstraktionsschritt entsteht ein gemischt-ganzzahliges lineares Programm (MILP) zur Topologievariation. Durch die Nutzung von stückweise linearer Optimierung kann die globale Optimalität des Systems hinsichtlich der definierten Funktion und Ziele garantiert werden, ohne dass Kompromisse hinsichtlich der Genauigkeit gemacht werden müssen. Dieser Schritt stellt den bisherigen „missing link“ zwischen Planung und Validierung bisheriger Auslegungsprinzipien dar. Die innerhalb des Optimierungsmodells optimalen Lösungen werden physikalisch durch 0-dimensionale Modelle, z.B. mittels des Sprachstandards Modelica überprüft. Zur Validierung dienen konventionelle dreidimensionale Simulationen oder Versuche, bevor das System realisiert wird.

Low power linear drives (P < 5 kW) are used in a wide field of applications, ranging from process automation via wind power plants, automotive applications to plastic machinery. Conventional valve controlled hydraulic drives are increasingly displaced by electromechanical drives due to several advantages (good energy-efficiency, less required space, low maintenance effort, easy plug and play connectivity). In recent years, new energy-efficient electrohydraulic compact drives came up, which improve user-friendliness of hydraulic drives significantly. Configured as speed-controlled Turn-Key-Assembly these compact drives combine the advantages of both electromechanical drives and hydraulic drives (reliability, robustness, large forces, good overload protection) and accordingly improve the competitiveness of hydraulic drives.

In the recent past, investigations on electrohydraulic compact drives were carried out at Dresden Institute of Fluid Power augmentively. After investigating systematically circuit variants as well as static, dynamic and efficiency performance of preferred variants, the next important step is to investigate the thermoenergetic behaviour. In order to guarantuee a temperature stable process of electrohydraulic compact drives the knowledge of the thermo energetic properties is essential. Owing to the complexity of thermal processes a lumped parameter simulation model is appropriate, in order to simulate, analyze and optimize the thermo energetic behaviour of electrohydraulic compact drives with reasonably effort.

Due to the good energy-efficiency of the compact drive a cooling aggregate is not installed. As a consequence, the thermal behaviour is governerd by the interaction between heat input (via dissipated energy) and the passive heat output (via free convevtion and radiation). Moreover, in comparison with conventional hydraulic systems electrohydaulic compact drives are only equipped with a small oil volume. This leads to a high sensitivity to incoming heat flows. Approaches known from literature, which describe the thermo energetic behaviour of conventional hydraulic systems with lumped parameters, can not be transferred on electrohydraulic compact drives. Main reasons for this are the complex 3-dimensional interferences between the highly integrated components and the passive heat transfer. An appropriate way to simulate the thermo energetic behaviour of electrohydraulic compact drives with lumped parameters is not known yet.

The proposed paper highlights the thermoenergetic behaviour of an electrohydraulic compact drive, which was built up as a demonstrator in the laboratory. Based on measurements of energy-efficiency an analysis of heat sources, heat flows and heat sinks is done. Derived from the analytic description of the components thermal behaviour a thermo-hydraulic simulation model with lumped parameters was built up and validated by measurements on the demonstrator. Besides thermo elements a thermographic camera was used to detect the specific temperatures in different regions of the compact drive in detail.

The results of the measurements show the thermoenergetic behaviour of the compact drive in different operating cycles. However, in comparison with simulation results some divergences appear. It can be shown, which differences occur between model and experiment and which accuracy can be achieved with the present knowledge and methods. New approaches for the investigation and simulation of the thermoenergetic behaviour of electrohydraulic compact drives are proposed.

The construction machinery is widely used in all kinds of earthwork construction, but due to the low efficiency of hydraulic systems, some energy regeneration should be put forward. The paper will introduce a novel potential energy regeneration system that based on electric-hybrid system. Potential energy regeneration system which shares an electrical storage component with power system, can effectively improve the energy utilization without additional expense. However the traditional potential energy regeneration system results in poor dynamic characteristic. A novel potential energy regeneration system which combine throttle-governing and regeneration devices, can guarantee the dynamic characteristic of system, and realize the maximum efficiency of energy recovery. For its simple layout, it can be applied to different actuator, the paper will analyze the novel potential energy regeneration system in theory in comparison to throttle-governing system and traditional potential energy regeneration system, finally some simulations will be presented,the simulation results show the effectiveness and dynamic characteristics of novel potential energy regeneration.

To provide an efficient rectification solution for the linear piston pump, a collaborating construction is developed in this paper. The direct drive cell is the fundamental structure of the pump, consisting of a piston and a spool valve, whose rod and spool are integrated and driven linearly. A functional pump module should be constructed by the cells based on the collaborating rectification principles, which are summarized in the form of theorem, and mathematical formulated and proved. Principles analysis shows that a module should be constructed by at least two cells with a valid collaborating rectification construction, and a multi-cell module should be constructed based on two-cell modules. Kinematic flow rate characteristics analysis of a typical two-cell module shows that as it makes full use of signal and energy routes, the collaborating construction is efficient and flexible.

Inside axial piston pumps and motors, the design of the slipper-swashplate lubrication interface requires a delicate balance between performance and efficiency. Moreover, elastohydrodynamic effects which vary with pump speed, pressure, and displacement complicate the matter further. To create a slipper design which will be simultaneously efficient and not exhibit long-term wearing requires significant design iterations and testing. Previously this testing was conducted on prototype manufactured pumps consuming great time and expense.

Now, thanks to many years of focused research, an advanced fluid-structure-thermal numerical model has been developed which is able to accurately simulate the greatest unknown: the transient fluid film thickness between the slipper and swashplate at any pump operating condition. Using this information, leakage, friction, and wear indications between the slipper and swashplate are calculated for steady-state operation of the pump or motor. Because of the fidelity and sensitivity of this numerical slipper-swashplate lubrication model, there is now the potential to significantly reduce the cost and time required to create new pump designs by subsisting physical prototyping with parallelized virtual prototyping.

To validate the accuracy of the newly developed slipper-swashplate model, for the first time a test rig has been constructed which directly measures the fluid film thickness between the slipper and swashplate of a commercially produced axial piston machine. Great care has been taken to minimize the pump modifications necessitated by the capacitive sensor installation into the swashplate. This paper will conclude by presenting a comparison between the simulated and measured fluid film thicknesses over a range of pump operating conditions.

Radialwellendichtringe (RWDR) sind dynamische Dichtungen und werden zur Abdichtung rotierender Wellen und Achsen gegen verschiedene Medien eingesetzt. Im Betrieb sollte der RWDR idealerweise reibungsarm sein, wenig verschleißen und gleichzeitig keine Leckage zulassen. Beim Erreichen dieser Ziele kommt erschwerend hinzu, dass der RWDR in der Anwendung den unterschiedlichsten Betriebsbedingungen z.B. erhöhten Temperaturen und aggressiven Medien ausgesetzt wird. Außerdem treten zusätzlich mechanische Belastungen infolge von statischen Wellenexzentrizitäten durch Fertigungs- und Montagetoleranzen, sowie dynamische Wellenschwingungen auf.
Unter solchen mechanischen Belastungen wurden bisher Untersuchungen zu dem Reibmoment und Leckageverhalten von RWDR gemacht [1]. Das Reibmoment sank mit steigender Frequenz und Amplitude der Wellenauslenkung. Das fallende Reibmoment war jedoch meistens mit einer zunehmenden Leckagerate verbunden. Zu den Auswirkungen auf den RWDR-Verschleiß hingegen sind den Autoren keine bisherigen Veröffentlichungen bekannt.
Im Rahmen dieses vorgeschlagenen Beitrags wird daher untersucht, wie sich statische und dynamische Wellenauslenkungen in radialer Richtung auf das Verschleißverhalten von RWDR auswirken. Die experimentellen Untersuchungen werden bei verschiedenen statischen Wellenversätzen, sowie Wellenschwingungsfrequenzen und -amplituden am „Grenzleistungsprüfstand“, welcher am MEGT entwickelt wurde, durchgeführt. Das Verschleißvolumen der gelaufenen RWDR wird optisch durch Vergleich der neuen und verschlissen Dichtkantenkontur ermittelt.
Aus den Ergebnissen des Beitrags lassen sich konstruktive Empfehlungen zur Wellenauslegung bzw. –lagerung mit dem Ziel ableiten, dass der RWDR zuverlässig abdichtet, aber zugleich auch wenig verschleißt und somit eine höhere Lebensdauer aufweist.

[1] Péteri, S.; Sauer, B.: Dichtheit von dynamisch belasteten Radialwellendichtrin-gen bei verschiedenen Temperaturen. 12th International Sealing Conference. 10-11 September 2002, Stuttgart.

Axially balanced lateral bushes are essential components found in External Gear Machines (EGM) used for high pressure applications. These lateral bushes are floating elements which are essential for efficient and reliable performance for EGMs. The lateral bushes are hydrostatically loaded in order to achieve a lubricating gap film thickness which allows machine operation with low leakage losses as well low levels friction and wear. The present authors have presented a fully coupled fluid-structure-thermal interaction (FSTI) model which can accurately predict the performance of lateral gap in terms of lubricating gap film thickness, pressure, viscous friction and volumetric leakage losses [1-3]. In addition, the FSTI model has been validated using experimental leakage measurements on an EGM prototype with the model showing a good correlation in terms of trends with changing operating conditions, as well predicting the magnitude of volumetric leakage flows accurately [4].
The present work is focused on a more detailed experimental investigation which has been carried out aimed at measuring the lateral gap lubricant film thickness in a more direct manner. The lateral gap film thickness is typically of the order of microns and this makes a direct measurement of the lateral gap height extremely challenging using traditional proximity measuring techniques such as using LVDTs. Optical measurement methods of proximity have the ability to measure micron ranges but require an optically clear environment not present in EGMs. However, due the dielectric nature of hydraulic mineral oils proximity measurements using highly sensitive capacitive sensors were found to be effective.
The experimental measurements were performed on a prototype EGM, where the capacitive sensors were installed on the pump body. In addition to the film thickness measurements con ducted using the capacitive sensors - detailed measurements of the EGM body were conducted using a coordinate measuring machine. This enabled the final measurement of the lateral lubricating gap film thickness on the prototype EGM. Experimental results are presented for a wide range operating conditions for the prototype EGM along with detailed discussion regarding the observed film thickness trends. Additional insight is presented by comparing the experimental measurements to results from the FSTI model of the lateral gaps.


1. Dhar S. and Vacca A. “A Novel CFD- Axial Motion Coupled Model for the Axial Balance of Lateral Bushings in External Gear Machines”,Simulation and Modeling Practice and Theory (Elsevier), 2012.
2. Dhar S., Vacca A. and Lettini A. “A Fluid – Structure Interaction model to analyze Axial Balance in External Gear Machines”, 8th IFK International Fluid Power Conference, Dresden, Germany, 2012
3. Dhar S., Vacca A. and Lettini A. “A Novel Elastohydrodynamic Model for the Lubricating Gaps in External Gear Machines: Evaluation of Axial Balance”, 7th FPNI PhD. Symposium on Fluid Power, Reggio Emilia, Italy, 2012
4. Dhar, S. and Vacca, A. “A Fluid Structure Interaction-EHD Model of the Lubricating Gaps in External Gear Machines: Formulation and Validation”, Tribology International (Elsevier), 2013.

Hydropneumatic accumulators are widely used in systems to restrain pressure pulsation and absorb transient impact. The container of an accumulator is divided into two parts as gas chamber and oil chamber by a piston or bladder interface. The charge gas (usually nitrogen) is compressed by the hydraulic oil and expands when the oil pressure depressed. The heat transfer process of charging gas is usually treated as isothermal or adiabatic process according to its working condition. In aviation or aerospace environment, ambient temperature of a hydraulic accumulator varies in a very large range, the pressure characteristics of the accumulator is influenced significantly by the dynamic gas temperature which is determined by the heat exchange between the accumulator and its ambient. This article presents a thermo-mechanical-coupling model of a hydraulic piston accumulator based on theories of energy conservation and heat transfer. Compare to traditional hydropneumatic accumulator model treating nitrogen as ideal gas, real-time heat exchange between nitrogen and shell and ambient, then the item caused by dynamic temperature of nitrogen is considered in the pressure reflection in the coupling model. Container materials, structure parameters and working conditions are discussed to investigate the dynamic pressure performance of a piston accumulator using in a hydraulic brake subsystem of X-type aircraft.

Pilot stage of servovalves and high response valves is mostly of open center type such as flapper nozzle or jet pipe valves. This paper introduces a pilot valve of closed center type and examines its dynamic performance. The valve mainly consists of a main spool, and a through the spool shaft as a pilot stage. The pilot orifices are formed by the pilot shaft angular input displacement, and closed by the main spool linear movement, thus the spool follows the pilot shaft input without need to extra feedback loops. Pilot stage of closed center type consumes very small amount of on demand pilot oil during the main spool movement only.
The simulation shows outstanding step and frequency response. This new valve enjoys high stability with strong immunity against disturbances, flow forces, and negative damping. The high pilot pressure and flow gains enable replacing three or more stages valves with valves of two stages only.

Die stetige Weiterentwicklung von Computer- und Simulationskapazitäten ermöglicht die Abbildung von immer komplexeren hydraulischen Systemen bei gleichzeitiger Erhöhung der Simulationsgüte. In vielen Anwendungsfällen zeigt sich, dass die erhöhten Kapazitäten nicht zur Reduzierung der Rechenzeit, sondern zur Erhöhung der Modellkomplexität und Vorhersagegenauigkeit verwendet werden. Der effiziente Einsatz der gegebenen Ressourcen bleibt somit in den meisten Fällen eine der wichtigsten Randbedingungen. Aus dem Bereich von physikalischen Experimenten sind verschiedene klassische statistische Methoden bekannt (z.B. statistische Versuchsplanung), die häufig auch im Bereich von Computerexperimenten eingesetzt werden. Diese Methoden können jedoch die speziellen Eigenschaften von Computersimulationen, wie zum Beispiel keine Messstreuung in Simulationen, nicht ausnutzen, wodurch die vorhandenen Ressourcen und simulationstechnischen Möglichkeiten bei Weitem nicht ausgeschöpft werden. Über die letzten Jahre hinweg wurden spezialisierte Methoden im Bereich Versuchsplanung, Meta-Modellierung, Analyse und Optimierung entwickelt, welche bei einem gleichzeitigen Einsatz maximale Informationen und beste Ergebnisse erzielen.
Die hier geplante Präsentation zeigt ein statistisch sinnvolles Gesamtkonzept von Versuchsplanung über Modellbildung und Analyse bis hin zur Systemoptimierung zum Einsatz bei Computerexperimenten.

This paper discusses the influence of the internal geometry on the behavior of spool directional valves. This study is based on both the flow modeling on control orifices and internal channels and test carried out with an overspeed sensor and a distributing valve applied to hydroelectric turbine control. On hydroelectric power plants, several hydraulic components of the speed governor are particularly designed for this application, operating under unusual pressure and flow rate values when compared to industrial and mobile fields. This fact demands low-scale manufacturing of the components where these must meet the requirements of standards such as IEC 60308 and ISO 10770 series. These standards establish steady-state and dynamic characteristics that must be achieved under specific operate conditions, characterizing the hydraulic component. Aiming to support the analysis and design of directional on/off and continuous control valves, a model based on the principles of fluid mechanics have being developed which allows the study of the influence of internal geometry on the behavior of both flow rates and pressures. Features like control orifice shapes, radial clearances, and internal channel sizes are considered in this analysis. The simulations are carried out by Matlab/Simulink where the model is applied to the analysis of a directional valve operating as a turbine overspeed sensor and a 2,500 L/min distributing valve. Therefore, it was possible to analyze the model robustness on different size of valves. The theoretical results are compared with the experimental data obtained in laboratory considering the specifications from international standards mentioned above. Some characteristics such hysteresis, dead zone, internal leakage, stabilization test time are evaluated under different internal geometry parameters that leads guidelines to be taken during performance tests. With the validated model, different directional valve configurations applicable to discrete control (on/off) or continuous control (such as proportional valves) can be evaluated. The knowledge about these important phenomena that influence valve characteristic curves such load pressure, internal leakage, and control flow rate depending on spool displacement and supply pressure is systematized. These results can help both professionals involved on operation and maintenance by the identification of possible valve failing causes and design engineers on the definition of dimensional tolerances.

In recent years, a trend towards speed-variable pump drives has become apparent. By using an axial piston pump with variable displacement, motor speed and volume flow can be decoupled providing a degree of freedom for controlling hydraulic processes.
This degree of freedom has been used in prior studies on a holistic analysis of static losses in electro-hydraulic drive systems to increase energy efficiency. By developing an operating-point-oriented motor speed feed forward control, energy savings of over 20% for static and quasi-static process cycles were proven in comparison to pure speed-variable or pure displacement-variable control strategies.
At the same time, however, a crucial shortcoming of the static loss model had to be observed in dynamic cycles. Fast acceleration sequences lead to increased copper losses in the electric drive, which can dominate the estimated energy savings when following the energy optimal operation points. As a result, the energy-optimized two-variable control led to increased energy consumption in dynamic injection molding processes, when it was compared to traditional process control with a variable-displacement-pump at constant speed.
In this work, the aforementioned problem will be countered with a model predictive control approach. For that purpose, a time-discrete dynamic loss model of all drive components was formulated. In contrast to the conventional operating-point-oriented optimization a new cycle-oriented optimization can be introduced, minimizing the energy consumption for any hydraulic cycle. In the model predictive approach a known, recurring control task is transformed into an equivalent mathematical optimization problem for the entire cycle. By means of formulated constraints, the required process dynamics, such as considering the physical limits of the drive components, can also be ensured.
In simulations with the new, validated dynamic loss models of all subcomponents energy savings of up to 30% were achieved in comparison to the known static approach to efficiency optimization. In particular, the functional verification of the model predictive concept for highly dynamic processes was proved, in which the static optimization became inefficient.

Parallel digital hydraulic valves are still in an early stage in their development, but in several cases they have already proven to produce superior results compared to traditional technologies. Building one control edge, or a digital flow control unit (DFCU), for a high performance digital valve system requires at least seven, preferably many more, fast on/off-valves. The valves must be integrated into a small package in order for the digital valve systems to be competitive against traditional valves. The currently sold commercial valves are not suitable to be used in digital valve systems since the valves are generally too large and their response time is poor. Therefore it is necessary to develop smaller and faster on/off-valves which can be effectively integrated into a compact package.

Small valves require a small and fast but sufficiently powerful actuator. The aim for this research is to investigate the factors affecting the response time and force output of a very small and fast electromagnetic actuator, which is designed to be used as the pilot valve actuator in a digital valve system. The selected actuator type in this research is a plunger type solenoid. The diameter of the actuator is approximately 10 mm and height about 15 mm.

Because the response time of the actuator is approximately 0,5 milliseconds, the dynamic electromagnetic effects are a major factor in delaying the response. The most important electromagnetic phenomena are the inductance of the solenoid coil and the eddy currents formed in the core material of the solenoid. These factors are dependent on the type of material and the geometry of the solenoid.

In this research, a detailed finite element method (FEM) model of the solenoid is built using Comsol Multiphysics software. The model is used to simulate the effects of different geometries and materials for the magnetic circuit of the solenoid. The results from the simulations are verified by building a prototype according to the FEM model. The prototype will be manufactured from three different materials: magnetically soft low carbon steel, martensitic stainless steel and a soft magnetic composite. The prototypes will be tested with a number of coils with different numbers of turns.

The results of this research are expected to demonstrate which material, coil and geometry parameters are important when designing a very fast acting miniature solenoid actuator. As a result it will be possible to improve the performance and energy efficiency of the actuators while keeping their size as small as possible.

This paper introduces an innovative high performance actuation system for hydraulic valve based on the coupling of energy storage components. The momentum coupling valve (MCV) allows the moving component of a valve (poppet, spool etc.) to be momentarily coupled and decoupled with an already moving mass to produce linear motion, rather than accelerating and decelerating actuator and valve components simultaneously, as in traditional solenoid, armature, and spool combinations. Improvements in system efficiency and dynamic performance are needed in hydraulics, and high speed valves are a key enabler. They allow for greater control bandwidth, reduced metering losses, and can enable new system architectures in digital hydraulics such as switching control and digital pump/motors. The general coupling concept can be applied to many different design configurations. Coupling techniques includes piezoelectric actuators, magneto-rheological fluid, and electromagnetic couplers. In this paper the features, strengths, and weaknesses of each configuration will be examined. This paper presents the design and testing of a prototype using a magneto-rheological fluid coupler to validate a coupled-physics model that was developed early in the design phase. The experimental testing was conducted to validate the concept of a momentum coupling mechanism to achieve high speed valves for digital hydraulic applications.

ABSTRACT
Digital hydraulic valve systems have been studied much during the last decade. Most theoretical advantages of the valve system which utilizes only parallel connected on/off valves have been verified with test systems. However, experimental research has been concentrated on the valve systems where volume flows of the valves are adjusted according to power of two. An alternative approach is to use a wide array of one size miniaturized on/off valves. Previous research indicates that this approach has a lot of benefits. Although lots of benefits compared to “binary coded” approach, the benefits of this approach have not been verified with experimental studies. The reason is the lack of suitable miniature valve which is sufficient low cost and usable in this kind of valve system. To fill this demand miniaturized on/off valves have been developed at Tampere University of Technology. The main purpose of this paper is to present the concept of the microhydraulic valve system utilizing the newest prototype of the miniaturized on/off valve and laminated manifold in order to increase the packing density of the valves and also to decrease the manufacturing costs of the manifold.
A multitude of valves bring some challenges for model based controller which is the main controller approach in the digital hydraulics. Assuming that, the model of the valve system in the controller has to involve individual parameters for every single valve, the model become quite heavy. To avoid this issue, the controller could use same parameters for every single valve. In this paper it is shown with simulations, that this approach of using mean valued parameters, have not significant effect on control performance compared to the controller with individual parameters for every single valve.

Die Anforderungen an direktgesteuerte pneumatische Schaltventile und deren elektromagnetische Aktoren erhöhen sich stetig, insbesondere in Bezug auf Bauraum, Energieeffizienz und Herstellungskosten. Jedoch sind das Entwicklungspotenzial für die angestrebten Verbesserungen nicht ausgeschöpft, die volle technisch mögliche Leistungsfähigkeit der elektromagnetischen Aktoren bisher nicht bekannt und der Realisierungsaufwand zum Erreichen bestimmter Leistungsdaten nicht bewertbar.
Das Ziel der vorgestellten Arbeiten besteht darin, die Einflüsse aller wesentlichen Konstruktionsparameter auf die Leistungsfähigkeit pneumatischer Schaltventile zu berechnen und systematisch zu analysieren. Um die interessanten Leistungskennzahlen zu bestimmen, sind transiente Berechnungen notwendig. Daher wurde für die Studien eine typische Magnetbauform ausgewählt und ein domänenübergreifendes Netzwerkmodell mit konzentrierten Parametern implementiert. Die Netzwerkelemente, wie elektrische und magnetische Widerstände, werden aus den Konstruktionsdaten bestimmt und die Zusammenhänge in einem eigenen Typ hinterlegt. Dadurch sind die Geometrieparameter als Eingangsgrößen für Parameterstudien verfügbar. Bei der Validierung des Simulationsmodells anhand eines Beispielventils wurde eine gute Übereinstimmung im statischen und transienten Verhalten erreicht.
Um die umfangreichen Parameterstudien effizient durchzuführen, wurde das Simulationsmodell in ein Optimierungswerkzeug eingebunden, welches Methoden der statistischen Versuchsplanung bereitstellt. Eine Sensitivitätsanalyse aller Parameter mit Normalverteilung zeigte, dass zwar der Parameterraum reduziert werden kann, jedoch starke Wechselwirkungen zwischen den Parametern existieren. Dies bedeutet, dass Studien einzelner Parameter nicht zielführend sind. Jedoch bietet sich eine Sensitivitätsanalyse mit Gleichverteilung an, bei der physikalisch-technische Grenzen der Fertigung mit dem Größt-/ Kleinstmaß abgebildet werden. Auf diese Weise wird der gesamte realisierbare Parameterraum berücksichtigt.
Als Ergebnis dieser Studien können die Verbesserungspotenziale und Leistungsgrenzen der Schaltmagnete aufgezeigt werden. Dazu wurden für die Auswertung der Parameterstudien aus den Leistungsdaten sinnvolle Ziel- und Vergleichskriterien abgeleitet. Zielkriterien sind beispielsweise Leistungskennzahlen wie die Schaltzeit ts, der Wirkungsgrad ηges und die minimal notwendige Halteleistung Pmin. Vergleichskriterien sind beispielsweise das Anreihmaß, das Aspektverhältnis des Elektromagneten L/B und der Ankerhub xA. Auf diese Weise werden die Bestwerte der Parameterstudien für jedes Zielkriterium gefunden und die entsprechenden konstruktiven Dimensionen und die elektrischen Anforderungen identifiziert. Diese Daten ermöglichen das Abschätzen des notwendigen Realisierungsaufwands für das Erreichen bestimmter Entwicklungsziele.
Insgesamt kann formuliert werden, dass für eine weitere Miniaturisierung der Schaltmagnete die Integration einer Elektronik zur Leistungsabsenkung notwendig ist, da dadurch die Eigenerwärmung deutlich reduziert werden kann. Weiterhin sind auch flache Elektromagnete ebenso leistungsfähig wie konventionelle hohe Magnetbauformen. Es erscheint daher sinnvoll, neuartige Fertigungsverfahren wie den 3D-Siebdruck einzusetzen, welche sich durch besonders hohe Ressourceneffizienz und hohe Fertigungsgenauigkeit auszeichnen.
Aus den gefundenen Bestwerten wurde eine Variante für den Aufbau eines Demonstrators ausgewählt. Sie zeichnet sich durch die kleinste Schaltzeit tS, ein kleines Volumen Vmag und ein geringes Anreihmaß aus. Für die Fertigung als Funktionsmuster und die experimentellen Untersuchungen musste die Konstruktion aus der Parameterstudie leicht modifiziert werden, wodurch sich auch moderate Änderungen der Leistungsdaten ergeben. Die experimentelle Analyse konnte das simulationstechnisch berechnete Verhalten sehr gut bestätigen und somit die Realisierbarkeit der Verbesserungsvorschläge demonstrieren.

Reason for the slow adaptation of new greener technologies is often the need for large modifications in products or systems. Different kind of regenerative pump-motor transformers might give an optimal solution for the energy efficiency of upcoming hydraulic systems, but the authors’ viewpoint is that it will demand decades before the technology is going to be widely adopted. On the other hand especially the industrial hydraulic systems have often very long life-times and the large scale of the system often makes it unprofitable to fully rebuild the system for improved energy-efficiency.

In order to improve the existing industrial and mobile hydraulic systems in a shorter time range, retrofittable digital hydraulic valve concept is presented to replace the old proportional and servo valves. In this paper advantages of three different digital valve system configurations are analyzed. Configurations include utilization of a pressurized tank line and a common regenerative pressure line attached to valve block through logic valves. Analytical study involves steady-state energy-efficiency comparison to a traditional proportional LS-system with multiple actuators. As the improvements are highly dependent on the system cycle and power distribution during the cycle, worst-case and optimal improvements are presented and velocity and force levels are realistically weighted according to an example data presented in literature. Also the possibility to improve productivity by improving old valve technology by fast actuating digital valves and technical challenges in retrofitting are discussed.

This paper presents an original concept valve characterized by two independent actuating mechanisms controlling the metering area, the first one is realized with a rotating actuator, the second one with translating one.
The working principle of state of art proportional valves is based on the linear motion of a spool or a poppet, the edges of the moving part are coupled with the edges of the body in such way that a proper metering area is obtained.
The valve hereinafter presented has a two moving parts: a rotating sleeve and a translating spool, the flow area is determined according to the mutual position between the holes on the sleeve and the edges on the spool. The metering area is then related both to the movement of the spool similarly to a traditional spool valve, and to the rotary movement of the sleeve controlled by a torque motor, a DC motor o a rotary coil, as a function of force, speed and precision requested by the application.
The metering area is the result of two actuators position, and the resulting control is linearly depending by two PWM signals, both controlled by a microcontroller. The set of values available to control the actual metering area is then composed by a 10 or 12 bit data, used to generate the PWM duty cycle of the coil current control connected to the spool, plus the 10 or 12 bit data, used to generate the PWM duty cycle of the rotary motor coil current control connected to the cylinder, resulting in a 1024 or 4096 per 1024 or 4096 bi-dimensional control area, as a function of the chosen microcontroller. The metering control precision is virtually quadratic in respect to the traditional valve spool position control method.
Another big advantage is the flexibility, as an unique valve design can be used for several application due to the possibility to realize different Functions of Area with the two combined controls and without the need for special spool design and costly notches adjusting.
The valve design can be realized allowing:
1. AND-logical control of the two actuators, in relation to the metering area, enabling a highly safe normally closed valve,
2. OR-logical control, enabling a very fast valve,
3. Or different type of controls, like following controls, where the metering area can be obtained with different combination of relative position of the two actuators.
Moreover the new design of the valve allow special positions in order to assure the functionality (emergency closing or opening of the metering area) even in case of failure or blocking of one of the two actuators.
From the functional safety point of view The valve can assure a limited functionality, thus presenting a fail operational characteristic, or even a fully functionality, with limited precision, due to the control of only one of the actuators, thus presenting a fault tolerance to the faults.
From the functional safety point of view The valve can assure a limited functionality, thus presenting a fail operational characteristic, or even a fully functionality, with limited precision, due to the control of only one of the actuators, thus presenting a fault tolerance to the faults.
Besides, the valve respects two of the most important principles of the design for safety: redundancy and diversity, offering the functionality normally obtained using two valves, with a limited space and weight.
The paper will show the valve design, highlighting the peculiar characteristics of the mechanical solution, and finally a functional safety analysis will be drawn out.
In the paper the control strategies and the opportunities offered by the new design will be discussed, with the aid of some example, focusing on control precision and valve configuration. As an example, the advantages of some X-by-Wire application will be discussed, especially for steer by wire, and brake by wire, where the main function can’t be lost due to a single fault.
The paper will also show the different actuators characteristics, comparing force and dynamic performance.

Underwater manipulators are widely used in ocean development. Nowadays, oil hydraulic cylinders and motors are the main drives of underwater manipulators. Although the oil hydraulic components and technologies are relatively mature, there are still some disadvantages:
1. Susceptible to underwater environment, especially the pollution of piston rods and hydraulic motor shafts and the water and oil leakage from each other;
2. Not up to extreme miniaturization and light weight;
3. Poor bio-imitability and controllability.
So the water hydraulic artificial muscle is proposed to overcome the above shortcomings. Compared with hydraulic cylinders and motors, the water hydraulic muscle has many advantages such as high ratio of output force and own mass, fast response, good bio-imitability and controllability, compatible with the underwater environment, and so on. It is needed to improve the strength of the water hydraulic artificial muscle for the application in underwater manipulator. As well, the pressure of the water hydraulic artificial muscle is increased to match the pressure range of water hydraulic components.
In this paper, the geometric construction and processing technique of high-strength artificial muscles are studied. The materials of the rubber hose, rayon mesh and end fitting were selected at first. Secondly, the structure and crimping process of end fittings are provided. And the main parameters of the rayon mesh are optimized through experiments. Due to the difference between work media employed in the water hydraulic artificial muscle and pneumatic artificial muscle, the driving processes and characteristics are different. Aiming to analyze the drive characteristics, a test system is designed for the water hydraulic artificial muscle. The theoretical relationship among the amount of contraction, pressure and output drawing force of the water hydraulic artificial muscle is tested and verified. These contribute to improvements of designs and researches on the water hydraulic artificial muscle control systems. Furthermore, the underwater manipulator which is facile, small-size, light-weight and compatible with the marine environment will be shown in front of the public.

Beitrag zur Innovation der hochdynamischen Messtechnik in der Ölhydraulik

Das schwingungsfähige hydraulische Antriebssystem enthält bekanntlich auch mechanische und elektrische Teilsysteme. Die dynamischen mechanischen und elektrischen Komponenten lassen sich gut durch lineare Dipole beschreiben. Zusätzlich fällt das sehr gute Marktangebot an hochdynamischen mechanischen und elektrischen Messgeräten zu den kohärenten Paaren von Drehmoment und Drehzahl (Kraft und Geschwindigkeit) sowie Spannung und Strom am Markt auf.

Dieses breite Sensorangebot hat bei elektrischen Antrieben zu einem bemerkenswerten Fortschritt von Beobachterkonzepten geführt. So kann beispielsweise für Windkraftanlagen mit maximaler Leistung von 5,3 MW der Prototyp bei Neuentwicklungen eingespart werden, weil das Zusammenspiel von dynamischen Spannungs- und Strommessungen eine Praxiserprobung schon am Modell ermöglicht.

Dagegen wird die vorausschauende theoretische Beurteilung des Betriebsverhaltens Hydraulischer Anlagen nicht nur durch den physikalisch bedingt komplizierten Zusammenhang zwischen den kohärenten dynamischen Größen Druck und Volumenstrom erschwert. Hinzu kommt noch, dass kein einziger praxisrelevanter hochdynamischer Volumenstromsensor preiswert am Markt angeboten wird und damit der kohärente dynamische Volumenstrom praktisch gar nicht gemessen werden kann. Messtechnisch gesehen „hinkt“ die Ölhydraulik somit eigentlich nur auf einem Bein.

Im Vortrag wird deshalb das verbesserte erprobte Konzept eines hochdynamischen kombinierten Druck-, Volumenstrom- und Temperatursensors vorgestellt. Der Sensoraufbau ohne bewegte Teile ist denkbar einfach. Ein Montagering mit Messfühlern kann direkt vor oder nach jeder hydraulischen Komponente über einen Flansch eingebaut werden. Der in beide Strömungsrichtungen symmetrische nahezu hydraulisch verlustfreie Messsteg mit den Fühlern sitzt diagonal im Montagering. An diesem befinden sich nur drei Heizdrähte (dynamischeTemperaturmessung, Richtungserkennung, das Hitzdrahtanemometerprinzip misst das diagonal gemittelte dynamische Gechwindigkeitsprofil) und ein Dünnschichtfilm (dynamische Druckmessung). Der Montagering, der Messsteg und die Flansche sind den Baugrößen zugeordnet. Dagegen sind die Verschraubung der Schnittstelle und die Elektronik nur in einer einzigen Ausführung erforderlich.

Das neu vorgestellte Konzept wurde bewusst nicht patentiert, um der schnellen Einführung des dringend benötigten dynamischen Volumenstromsensors und der hier empfohlenen Zusammenarbeit während der abschließenden Entwicklung keine unnötigen Hürden in den Weg zu stellen.

Die Einsatzvielfalt für die extensive Messgröße „dynamischer Volumenstrom“ ist naturgemäß sehr groß, aber in der Hydraulik noch kaum erprobt. Für elektrische Systeme sind dagegen viele Auswertungsverfahren dynamischer Ströme bekannt. In Anlehnung an diese Erfahrungen wird im Vortrag eine kurze systematische Übersicht von Einsatzmöglichkeiten in der Ölhydraulik im Haupt- und Leckölstrom gegeben.

So gehören Parameterbestimmungen im Onlinebetrieb sicher zu den wichtigsten hydraulischen Anwendungsmöglichkeiten. Aber auch das zeitsynchrone Auswerten hydraulischer und mechanischer Größen, die dynamische Temperaturmessung, die Bestimmung von Viskosität, von Kompressibilität, die Messung von Druck- und Volumenstößen, Flüssigkeitsschallbeurteilungen, das Darstellen von Umsteuervorgängen in Pumpen und Motoren, die Beurteilung des Kavitationsbeginns, das Generieren von p-V-Diagrammen, die Onlinemessung von Schallimpedanzen, von Pumpen - Quellpulsationen und von Fasenverschiebungen zwischen Druck- und Volumenstrompulsationen sowie das Condition Monitoring gehören zu den Einsatzmöglichkeiten

Abschließend werden in einem Leistungsheft die noch zu lösenden Entwicklungsaufgaben so erläutert, dass sich konkrete Berührungspunkte der Zusammenarbeit zwischen potentiellen Sensorherstellern, Anwendern und Forschungseinrichtungen ableiten lassen.

Various control strategies in digital hydraulics have been studied and published in the last years. Pulse Frequency Control (PFC) which – opposite to PWM – uses the pulse repeating frequency and not the pulse width as control input, is a fairly new control concept in digital hydraulics. PFC may be to be preferred if the hydraulic switching device can realize a very particular pulse in a favorable way, e.g. concerning energetic efficiency, simplicity and cost of components, or ease of component or control standardization.

This paper deals with the application of PFC to the control a hydraulic drive. It is assumed that a digital flow unit (e.g. digital pump) can realize only one particular flow pulse which can be repeated any time but not before the previous pulse is finished. As a consequence, the relative control resolution of a PFC-system is limited because of the fixed pulse quantity and the maximum repeating frequency. Since this pulsing may interact with the dynamics of the plant, the dynamics of the whole system with the PFC needs to be analyzed.

In a previous paper authors investigated a system comprising the digital flow unit and a hydraulic cylinder with an attached mass and a constant load. They found that oscillation can be largely reduced, if either the single pulse’s duration or the time span of two pulses is tuned to the eigenfrequencies of the drive. In this paper additional degrees of freedom in form of an elastic structure (e.g. an elastic beam) are added to the linear hydraulic drive which is pulse-frequency controlled. The dynamical response characteristics of such a multi degree of freedom system in PFC, the switching effort, and the achievable position accuracy in two different operating scenarios – a stepwise and a quasi continuous motion - are analyzed by mathematical modelling, simulation, analysis, and reasoning.

Earlier simulations as well as measurements have shown the potential of the Digital Hydraulic Power Management System (DHPMS). The machine can function as a pump, motor and transformer, and due to multiple independent outlets actuators with arbitrary pressure levels can be efficiently served. In addition, pre-compression and pressure release phases can be optimized for every point of the operation thanks to actively controlled on/off valves of the pumping pistons. Hence, the energy stored in compressed fluid is possible to be optimally utilized.

Displacement control using the DHPMS has also been studied recently. In the approach, the outlets of the DHPMS are connected directly to actuator ports without using any flow control valves. The direct control has been tested by measurements in the case of a lift cylinder of a mobile crane. A six-piston DHPMS with two independent outlets was used in the study and the results showed the technique to be valid despite of low number of the pumping pistons. Moreover, the system was capable to efficient energy-recovery. Controlling several actuators however, requires more DHPMS outlets.

In this study, a DHPMS with five outlets is modeled and a controller is created to directly control two actuators; a lift cylinder and tilt cylinder of a small excavator crane. A high pressure accumulator is attached to the fifth outlet and the accumulator energy is controlled to keep the prime mover energy at minimum. Simulation results show that the crane can be controlled smoothly also without position feedback of the cylinders. Even the chance in the load force direction does not deteriorate the velocity tracking as long as the cylinder back pressure is controlled. Furthermore, the system losses are significantly smaller than of that of the simulated LS-system.

By now, digital hydraulic concepts are widely accepted in the fluid power community.
However, the implementation of such solutions often requires an increased effort in control
design. Nonlinear model based control methods are particularly useful for digital fluid
power systems [1, 2].
This contribution is concerned with flatness based control for a class of simple digital
hydraulic drives based on an independent metering approach. As an example, a fixed-
displacement motor driving an inductive load with variable load torque is considered. The
motor is controlled by means of switching valves at both the inflow and the outflow port
allowing for driving as well as (non-regenerative) braking. Additionally, hydro-pneumatic
accumulators are connected to each port for pulsation smoothing.
For the resulting nonlinear multiple-input multiple-output problem, a flatness based
tracking controller involving a cavitation avoidance strategy is presented. The control
method proposed is applicable to both major digital hydraulic principles [3]: the fast
switching approach and the parallel connection approach. The design of a nonlinear load
observer is discussed, too. The control algorithms are illustrated by numerical simulation
results.

[1] Kogler H., ”The Hydraulic Buck Converter - Conceptual Study and Experiments,”
Dissertation, Johannes Kepler University, Linz, Austria, 2012.
[2] Hießl A., Plöckinger A., Winkler B., and Scheidl R., “Sliding Mode Control for
Digital Hydraulic Applications,” in Proc. 5th Workshop on Digital Fluid Power, Tampere,
DFP12. Finland, 2012, pp. 15–26.
[3] M. Linjama, “Digital fluid power – state of the art,” in Proc. 12th Scandinavian
Int. Conf. on Fluid Power, Tampere, SICFP12. Finland, 2011, pp 331–353.

At the 13th Mechatronics Forum International Conference in 2013 a novel Micro-Positioning System for a multi-spindle milling machine was presented. The purpose of this system is to compensate relative positioning errors of simultaneously operating spindles of multi spindle mill centres. In the first system, presented in 2013, a fast proportional control valve was used to fulfil the needs on reaction time and accuracy.

This paper reports about a digital hydraulic control concept for such micro-positioning drive replacing the proportional valve of the first system. The use of fast digital valves in combination with a standard industrial motion controller allows an increase of the accuracy compared to proportional valve control. The absolute position accuracy depends much more on the precision of the position sensor than on this drive’s performance limits and can be better than 1um. Besides the improved accuracy additional benefits of the digital drive system are: no drifting and energy savings because of a missing leakage and by far lower oil quality requirements.

Currently, the main market demands with regard to drive technology are energy efficiency, reduction of installation space and cost reductions. Depending on the application scenario, conventional throttle control based hydraulic systems (e.g. constant pressure supply and proportional valves as control element), often can not compete against electromechanical solutions with regard to the stated market demands. The use of variable-speed displacement unit drives (e.g. a fixed displacement unit being controlled by an electric motor and a frequency converter) can significantly improve the efficiency of the hydraulic system and therefore reduce the total cost of ownership as requested by the market. Nevertheless, such variable-speed displacement systems face challenges when the application demands cycles with little volume flow and high pressure levels at the same time. This results in an operating point with low rotational speed and a high driving torque, putting high loads on the components and thus generating heat and wear.

In 2011, Heino Försterling et al. presented a paper at DFP11 [Försterling, H., Stamm, E. and Roth, P. Tailored solutions limit complexity. The Fourth Workshop on Digital Fluid Power, 21st – 22nd September, 2011, Linz, Austria] stating the advantages (e.g. precise control and energy efficiency) of a 1bit digital hydraulics solution with ballistic-mode control.

The paper to be presented will demonstrate that the intelligent combination of the two system approaches (digital hydraulics throttle control, variable-speed displacement unit drive) is able to generate multiple application benefits. In such a system, the displacement unit drive is used to supply and control the high-speed process phase (high volume flows) as well as to charge a hydraulic accumulator. When entering the quasi-static process phase (e.g. applying a high force in a press application or fine-positioning resp. maintaining the reached target position for a longer time period), the digital hydraulics throttle control solely will be used to supply and control the hydraulic actuator. During this phase, the displacement unit drive is completely powered off, the needed hydraulic energy will be provided by the accumulator. The segmentation of the process phases and the use of the different control approaches in these phases results in the following advantages:
- High efficiency at high volume flows since a displacement unit is more efficient than throttle control
- Possibility to realize long pressure holding times without stressing the displacement unit / the electric motor
- The digital hydraulics on/off valve is a poppet valve and thus leakage free, making the quasi-static process phase very energy efficient.
- Very precise control (pressure, force, position) during quasi-static process phase through ballistic controlled digital hydraulic valve
- Considerable noise reduction during static process phase since displacement unit drive is switched off
- High overall system efficiency minimises the need for cooling capacity

In a general hydraulic system, a flexible high-pressure rubber hose is used. Until now, various researches have been reported about a viscoelastic pipe like a high-pressure rubber hose. It is necessary for the pressure propagation on a viscoelastic pipe that the viscoelastic characteristic of a pipe is taken into consideration. However, an exclusive use measurement bench is required for measurement of a viscoelastic character, in order to measure the flow of a high-pressure rubber hose by high response.
There, we devised how to calculate a viscoelastic character from measurement of only commercial pressure sensors, and we checked that it can measure satisfactorily. Thereby, measurement of viscoelastic character becomes simple, and to reflect to hydraulic system modeling becomes easier.

It is known that the characteristic of high-pressure rubber hose (Below, we call it a \"hose\") is expressed by viscoelastic characteristic, but the value of viscoelastic character of hose is unknown in many cases.
In general, the static value of bulk modulus of hose is shown by a manufacturer of hoses, which is measured by bulk modulus measurement bench. However, it is insufficient for expressing the dynamic characteristic. Because the value of viscoelastic character of hose is required.
Until now, there were the methods of determining viscoelastic character of hose in several ways, but the special equipment was needed in these ways. So it is generally difficult to get the viscoelastic character of hose. There, we considered how to determine the viscoelastic character of hose by easy method without special equipment.
In this method, it is necessary that the following properties are known.
1. The bulk modulus of hose, usually shown by a manufacturer of hose.
2. The bulk modulus of fluid.
In addition to the above properties, the experiment which measures the pressure response characteristic of a target hose is required. The experiment is the measurement of frequency response characteristic between the different two points on hydraulic line which consists in target hose, and the result is compared with the theoretical characteristic of the hose to determine the unknown property for the viscoelastic character.
The experiment for determining the viscoelastic property by this method is measurement of the pressure response which can become comparatively easy as compared with the method performed by other things.
In this paper, the method of determining viscoelastic character of hose is described, and the measurement results of viscoelastic character in several different kinds of hoses are shown.

A multi-degrees-of-freedom model for hydraulic pipeline systems
The dynamic behaviour of hydraulic pipelines has been modeled by the laminar flow of a compressible Newtonian fluid accounting for frequency-dependent friction [1]. The input-output relationship of this pipeline model is described by transcendental transfer functions, which have been approximated by rational fraction expressions for a single pipeline [2,3,4,5] and compound pipeline systems [6]. These modal approximations are intended for time-domain simulation or controller design; they have to be calculated individually for each transfer function.
In a recent article [7], the transfer functions between flow rate excitation and pressure response are determined for two points at arbitrary positions along a pipeline. Modal approximations are given such that the discretized model represents a damped multi-degrees-of freedom (MDOF) system with a flow rate excitation vector and a pressure response vector. For a system of several pipelines, an overall MDOF model can be assembled. It includes an approximation for each transfer function between flow rate excitation and pressure response. Eigenvalues and eigenvectors can readily be determined, offering an interpretation of the dynamic system behaviour.
In this paper, the MDOF model described in [7] is set up for a practical example. It consists of a pipeline network that connects a pump with two hydraulic cylinders. The network is excited by flow rate pulsations from the pump, and the MDOF model is used to simulate the resulting pressure pulsations in all system nodes. The eigenvalues and eigenvectors of the MDOF model reveal the natural frequencies and pressure mode shapes of the network. The high level of simulated pressure pulsations is explained by the fact that the network operates near a lightly damped resonance. Due to the existence of an equivalent mechanical MDOF model, heuristic methods from structural mechanics can be applied for effective system tuning. The relevant natural frequency is lowered by adding auxiliary pipelines at the pressure mode shape antinodes. Another simulation is made to determine the new pressure pulsations resulting from the original flow rate pulsations. It is demonstrated that the level of pressure pulsations is effectively reduced all over the network. Using the eigenvalue analysis, this can be done in a targeted way and a large number of trial simulations can be saved.
References
[1] A.F. D’Souza, R. Oldenburger, Dynamic response of fluid lines. Transactions of the ASME - Journal of Basic Engineering 86 (1964) 589-598.
[2] C.Y. Hsue, D.A. Hullender, Modal approximations for the fluid dynamics of hydraulic and pneumatic transmission lines, Fluid Transmission Line Dynamics, Special Publication for the ASME Winter Annual Meeting, Boston, Massachusetts, 1983, pp. 51-77.
[3] W.C. Yang, W.E. Tobler, Dissipative modal approximation of fluid transmission lines using linear friction model. Transactions of the ASME - Journal of Dynamic Systems, Measurement, and Control 113 (1991) 152-162.
[4] A. Almondo, M. Sorli, Time domain fluid transmission line modelling using a passivity preserving rational approximation of the frequency dependent transfer matrix. International Journal of Fluid Power 7 (2006) No.1 pp. 41-50.
[5] J. Mäkinen, R. Piché, A. Ellman, Fluid transmission line modeling using a variational method. Transactions of the ASME - Journal of Dynamic Systems, Measurement, and Control 122 (2000) 153-162.
[6] E. Kojima, M. Shinada, J. Yu, Development of accurate and practical simulation technique based on the modal approximations for fluid transients in compound fluid-line systems. International Journal of Fluid Power 3 (2002) No.2 pp. 5-15.
[7] G. Mikota, Modal analysis of hydraulic pipelines. Journal of Sound and Vibration (2013), http://dx.doi.org/10.1016/j.jsv.2013.02.021.

The important problem arising at operation of technological installations at the enterprises of energy, chemical, oil-processing and food industries is ensuring their reliability in conditions of high dynamic loadings of pipelines. The unsteady hydrodynamic processes occurring in pipeline highways at fast opening and closing of valves often lead to loss of sealing of pipelines’ joints, breakage of fittings and can become the reason of emergencies.
Such processes are especially dangerous to the pipelines made of polymeric materials being widely applied today, for example, in power plants. About 90 tanks-filters of chemical water purification with a capacity of 30 m3 with hundred meters of the pipeline 150mm diameter in which unsteady flow is occurred are operated in by-product recovery departments of large combined heat and power plants. Plastic pipes have high corrosion resistance, but smaller durability in comparison with steel pipes. Therefore research of dynamic processes in pipelines and development of approaches and devices which allow reducing intensity of dynamic loads of pipelines and fittings of technological installations is actual one.
In the paper, mathematical model of typical pipe system of processing plant, method and software for calculation of parameters of unsteady flow and dynamic loadings on pipework structure is developed. Methods and devices for reducing dynamic loadings are proposed. The simulation results of the model and efficiency of the devices proposed are experimentally verified.

Reduction of noise emissions of hydraulic systems has become essential during the recent years and nowadays has turned into inseparable part of the development process. A detailed knowledge about the vibrational behaviour of hydraulic hoses is very important in order to describe and simulate the dynamic behaviour of a complete hydraulic system.
Within a project at the Institute for Machine Tools of the University of Stuttgart, funded by the German Research Foundation (DFG), numerous investigations were carried out in order to identify the basic mechanisms of the structure-borne noise transmission through high pressure hydraulic hoses [Hei10].
Furthermore a finite element model of the high pressure hydraulic hose was built using the gained knowledge in the first project phase [Hei12].
In the current step of the project the FE-Model was updated applying the results of the conducted modal analysis. The experimental modal properties were compared with the simulative modal properties of the hydraulic hose using optimization looping. A sensitivity analysis and a mesh fineness study were carried out in order to achieve the optimal simulation performance of the FE-model. Then numerous calculations were carried out under different boundary conditions. Thus the dynamic behaviour of hydraulic hoses with different lengths, nominal diameters and reinforcement types can be simulated more quickly under different operating conditions compared to the laboratory testing time.
In the last step of this project the developed FE-model of the hydraulic hose was adapted to an existing model of a hydraulic aggregate in order to simulate the dynamic vibrational behaviour of a complete hydraulic system. The influence of the implemented FE-hose model on the dynamic behaviour of the complete hydraulic system was shown.

REFERENCES

/Hei10/ Heisel, U., Slavov, V., Investigation of the structure-borne noise transmission behaviour of hydraulic hoses. Workshop Proceedings, 7th International Fluid Power Conference, Aachen 2010, Vol.2, p.243-252

/Hei12/ Heisel, U., Slavov, V., Stehle, T., Structure-borne noise transmission behaviour of hydraulic hoses. Workshop Proceedings, 9th International Fluid Power Conference, Dresden 2012, Vol. 2, pp. 289 - 295.

New system optimization opportunities by simulation based line tuning

Caused by the functional principle of digital hydraulics there are a large number of very fast switching operations causing a high degree of pressure and flow pulsation in these systems. These pulsations can prove to be a problem because nowadays there are steadily rising standards for provided comfort, such as low noise and little vibration emissions, and efficiency besides the basic requirement of a stable system behavior. To meet these demands, system developers are often forced to elaborate active countermeasures in the form of complex control strategies. But there are also possibilities of passive influence, for example by adapting the line system. The problem here, however, is the high experimental effort that is required by these adjustments.

In this paper we discuss, by using the example of a hydraulic hose, how this experimental effort can be significantly reduced by using new simulation models and thus an easy form of system improvement is provided.

The necessary calculation methods have been developed considerably in recent years, however, the experimental verification has been paid little attention due to the costs and the huge expenditure of time. To close this gap, Saarland University of Applied Sciences HTWdS and Fluidon Gesellschaft für Fluidtechnik started the research cooperation „VeriSim“.

The realization takes place in four stages, starting with the validation of the measurement method and system through application of industrial recognized statistical methods, e.g. six-sigma. This measurement method is then used to characterize hydraulic components.
These results help to create a database of simulation models.
The next step is to extend these analyses from separate components to whole fluid line systems.
At the end there should be the possibility to simulate complex fluid line systems by linking the separate components the system consists of.

The possibilities offered by the use of these new simulation models are exemplarily shown at a hose connection. Based on the measurement data obtained, it is possible to identify the parameters determining the hoses transfer behavior and to make a statement about what kind of influence it is.

These influences are integrated in the component model. The user now can specify the hose model in the simulation according to its real component and calculate the expected system behavior.

Furthermore, the models can also be used to optimize the system performance by means of a parameter variation.

As a conclusion it can be derived that with these new models the development effort for new systems or the optimization of already existing ones can significantly be reduced. Especially for digital hydraulic systems this offers the opportunity for a quickly applicable and cost-saving passive form of influence on the system behavior by adjustment of its line system.

In the near future, these possibilities will be further enhanced by a steadily increasing number of available component models and improvement of the already existing models. It will also be possible to adjust models to specific user needs.